7 min · Written by a Crohn's patient on biologic therapy
Starting a biologic for Crohn's disease is a significant step. For many patients, it marks the point where the disease stops running the show — at least for a while. For others, it's the beginning of a long process of finding the right drug, the right dose, the right timing.
Understanding how biologics work doesn't replace your gastroenterologist's role. But it does change how you participate in your own care.
What Biologics Actually Do
Biologic therapies target specific proteins in the immune system that drive inflammation. Unlike traditional immunosuppressants that broadly suppress immune function, biologics are designed to block precise molecular pathways.
Anti-TNF therapies — infliximab (Remicade, Ixifi, and biosimilars), adalimumab (Humira and biosimilars), certolizumab pegol — target tumor necrosis factor alpha, a key driver of intestinal inflammation.
Anti-integrins — vedolizumab (Entyvio) — blocks the migration of immune cells specifically into the gut. This gut-selective mechanism means fewer systemic immune effects.
Anti-IL-12/23 — ustekinumab (Stelara) — targets interleukins 12 and 23. Often used in patients who didn't respond to anti-TNF therapy.
IL-23 inhibitors — risankizumab (Skyrizi), mirikizumab — newer biologics showing strong efficacy and increasingly available.
How Biologics Are Administered
Intravenous infusion — infliximab is given as a 2-hour IV infusion in a clinical setting. Standard schedule: doses at weeks 0, 2, and 6 (induction), then maintenance every 8 weeks — though many patients are adjusted to every 6 weeks based on trough levels.
Subcutaneous injection — adalimumab, ustekinumab (maintenance), and newer biologics are self-injected at home. Adalimumab is typically every two weeks; some patients move to weekly dosing.
Initial IV + subcutaneous maintenance — ustekinumab induction is a single IV dose, followed by subcutaneous maintenance injections every 8 weeks.
The Concept of Trough Levels
One of the most important — and least discussed — aspects of biologic therapy is therapeutic drug monitoring (TDM): measuring the concentration of the biologic in your blood at its lowest point (the trough), just before your next dose.
If your trough level is too low, the drug isn't maintaining adequate mucosal suppression. Symptoms return before your next dose — what patients often describe as "the last two weeks are always the hardest."
If your trough is too low, your gastroenterologist can increase the dose, shorten the interval between doses, or add an immunomodulator to boost drug levels.
If you notice your symptoms consistently worsen toward the end of your treatment cycle, bring this up explicitly. It's a measurable, correctable problem — not just something to endure.
Why Biologics Stop Working
Loss of response is one of the most common challenges in long-term biologic therapy. Two main mechanisms:
Pharmacokinetic loss of response — trough levels fall below the therapeutic threshold over time. Often correctable by dose escalation or interval adjustment.
Immunogenic loss of response — your immune system develops antibodies against the biologic, neutralizing it. Once high-level anti-drug antibodies are present, the drug is often permanently ineffective.
What increases antibody risk:
- Stopping and restarting the biologic
- Using the drug without an immunomodulator (for some anti-TNFs)
- Long gaps between doses
This is why stopping your biologic during a flare — even if it seems like it's "not working" — can permanently close that treatment option. The decision to stop or pause should always involve your gastroenterologist.
Combination Therapy: When and Why
Adding an immunomodulator (azathioprine, 6-mercaptopurine, or methotrexate) to a biologic is sometimes recommended, particularly with anti-TNF therapies. The rationale: immunomodulators can reduce the formation of anti-drug antibodies, helping maintain trough levels and extend the biologic's effectiveness.
The decision involves weighing added benefit against increased infection risk — it's an individualized decision, not a default.
Monitoring While on Biologic Therapy
- Blood tests — complete blood count, liver enzymes, CRP, and sometimes trough levels and anti-drug antibodies. Typically every 3–6 months in maintenance.
- Stool calprotectin — a non-invasive marker of intestinal inflammation, useful between endoscopies.
- Colonoscopy or imaging — to assess mucosal healing after induction and at intervals based on disease activity.
- Infections — biologics increase susceptibility to TB (screening required before starting), fungal, and opportunistic infections. Report unusual fever or persistent cough promptly.
- Vaccinations — live vaccines are contraindicated while on biologics. Make sure vaccines are up to date before starting.
What Patients Often Don't Know to Ask
- "What is my trough level?" — If you've been on infliximab or adalimumab for more than a year without this measurement, ask.
- "Do I have anti-drug antibodies?" — Especially relevant if the drug seems to be working less well.
- "What's the plan if this biologic loses efficacy?" — Better to understand in advance, not in the middle of a flare.
- "When should I contact you between appointments?" — Know the warning signs that warrant earlier contact.
Living With Long-Term Biologic Therapy
For many Crohn's patients, biologic therapy is a long-term commitment — years, sometimes decades. Understanding what that means in practice helps reduce anxiety and improve adherence.
The most common concerns patients have about long-term biologic use:
Infection risk. Biologics increase susceptibility to certain infections — particularly tuberculosis (screened before starting), fungal infections, and opportunistic infections. In practice, the absolute risk increase is modest for most patients. Standard precautions: stay current on vaccinations, report prolonged fever or unusual symptoms promptly, avoid close contact with active tuberculosis cases.
Cancer risk. Anti-TNF therapy has been associated with a small increased risk of lymphoma and skin cancer in some studies. This risk must be weighed against the well-documented risks of uncontrolled Crohn's inflammation. Your gastroenterologist monitors this as part of routine follow-up.
Pregnancy. Most biologics can be continued safely during pregnancy — the risk of uncontrolled IBD to mother and fetus is generally higher than the biologic risk. Discuss your specific situation with your gastroenterologist well before attempting to conceive.
When Biologics Aren't Enough: What Comes Next
If two or three biologics have failed — either from primary non-response or immunogenic loss of response — newer classes of therapies are available or in late-stage trials. Small molecule drugs (JAK inhibitors like upadacitinib, tofacitinib) work differently from biologics and can be effective in biologic-refractory disease. Discuss the full landscape of options with your gastroenterologist.
Frequently Asked Questions
- How long does it take for a biologic to work?
- Most patients see initial improvement within 2–4 weeks of starting induction. Full mucosal healing typically takes 3–6 months. Don't judge the drug's efficacy in the first few weeks.
- Can I stop my biologic if I go into remission?
- Some patients in deep, sustained remission successfully discontinue biologics — but relapse rates are significant. Stopping should only happen with careful monitoring and your gastroenterologist's guidance.
- Are biosimilars as effective as the original biologic?
- Yes — biosimilars approved for Crohn's disease have demonstrated comparable efficacy and safety to the originator drug. Switching is generally safe under medical supervision.
- Can I travel with my biologic medication?
- Yes, with preparation. Injectable biologics require refrigeration; travel cases and documentation from your gastroenterologist for airport security are essential. For infusion patients, treatment can sometimes be arranged at centers abroad — plan well in advance.
Diet also plays a role in managing Crohn's alongside treatment — see our guide on identifying your personal Crohn's trigger foods.
Biologic therapy has transformed outcomes for many Crohn's patients. For an overview of all approved options, the Crohn's & Colitis Foundation publishes an updated biologic therapy guide. Understanding how it works — and what to watch for — helps you be a more informed participant in a treatment that works best when it's actively monitored and adjusted.
